KR0172862B1 - Circuit for controlling the pulse width of switching source - Google Patents

Abstract

The present invention relates to a pulse width control circuit of a switching power supply device for supplying a stable output to a system circuit while protecting the switching power supply circuit in the event of a fluctuation of an input power supply voltage and a short power outage. The switching pulse width that is supplied for the first time in the circuit cannot be adjusted in the absence of current feedback, and the on-time of the switching power supply becomes large for the first time. In the present invention, the pulse width control circuit 19 compares the peak voltage and the reference voltage of the power supply unit 18 and the power supply unit 18 that supply a constant power, and the output and the triangular wave of the pulse width control circuit 19. The pulse generator 25 for comparing the output of the generator to generate pulses, and the switching shochu 10 according to the output level of the pulse generator 25. The on-time control of the problem is solved by providing a switching element driver 16 for adjusting the output of the magnetron (MG).

Description

Pulse width control circuit of switching power supply

1 is a system circuit diagram of a conventional switching power supply.

Figure 2 is an illustration of a switching power supply circuit with a pulse width control circuit of the present invention.

3 is a detailed circuit diagram of the main part of FIG. 2;

4 is a magnetron operating characteristic diagram of the present invention.

5 is a waveform diagram of each inverter part of FIG.

6 is an operational state waveform diagram of the switching element side of the present invention.

Figure 7 (a) is a reference diagram showing the correlation between the load and the commercial input of the present invention.

(b) is a table showing a load state according to the commercial pressure change in the circuit to which the present invention is applied.

8 is a block diagram showing another embodiment of the present invention.

9 is a circuit diagram showing an embodiment of FIG.

FIG. 10 is a waveform diagram of each part of FIG. 9. FIG.

* Explanation of symbols for main parts of the drawings

18, 40: power supply unit 19, 42: pulse width control circuit

41: pulse detection unit 25: pulse generator

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching power supply such as a microwave oven. In particular, the present invention relates to a pulse width control circuit of a switching power supply for supplying a stable output to a system circuit while protecting the switching power supply circuit in the event of fluctuations in input power supply voltage and a short interruption. It is about.

In general, a switching power supply is known as a switching mode power supply (SMPS), which is a device that converts commercial alternating current into direct current by an inverter circuit and then converts direct current into alternating current.

The conventional switching power supply is a rectification circuit (21) for rectifying and smoothing commercial alternating rules as shown in FIG. A predetermined output is detected by the switching transformer 23 for supplying the rectified power supply to the magnetron MG as a load by the switching element, the transistor 10 for switching the primary or coil of the switching transformer 23, and the switching transformer 23. And a detection comparator 22 to be compared to the pulse generator 25, a pulse generator 25 for providing a driving pulse to the transistor 10, and a switching element driver 16.

Thus Looking at the operational state of the prior art configured comparator (OP ₁₎ (-) where there is a triangular wave is input from the triangle wave generator (+) terminal is when the reference voltage is input by the output setting section (22a), a comparator (OP ₁ ) And compares the square wave to the pulse generator 25.

Then, since the pulse generator 25 generates a pulse to drive the switching element driver 16, the transistor 10 is turned on to supply power to the magnetron MG.

At this time, when a current flows in the coil L ₁ of the switching transformer 23, the current amount is detected by the resistor R ₁ and input to the negative terminal of the comparator OP ₁ .

Therefore, the comparator OP ₁ compares the input voltage of this (-) stage with the set voltage of the (+) stage, and outputs a high or low level, thereby charging or discharging the voltage level of the (+) stage of the comparator (OP ₁ ). The pulse width can be adjusted, thereby adjusting the supply output of the magnetron MG.

However, in such a prior art, the switching pulse width initially supplied from the pulse generator 25 cannot be adjusted in a state in which no current feedback is made, and thus the on time of the switching power supply is initially increased so that the switching element and The current and voltage values of the transformer are not only easy to exceed the standard values, but also have the drawback of causing damage or destruction of system circuit elements.

In addition, the pulse width is increased in the instantaneous power failure lamp during the circuit operation in the absence of current feedback, bringing the above drawbacks.

Disclosure of Invention The present invention has been made in view of the above-mentioned drawbacks, and an object thereof is to provide a pulse width control circuit of a switching power supply that enables the switch to operate safely in the early stages of power generation and when a power outage or an overvoltage is applied. .

Hereinafter, an embodiment of the present invention for achieving this purpose will be described in detail by the accompanying drawings.

2 shows a switching control device equipped with a pulse width control circuit of the present invention, a power supply unit 18 for converting a commercial AC source into a direct current, and a pulse for controlling pulse width by receiving driving power from the power supply unit 18. A width control circuit 19, a pulse generator 25 connected to the microcomputer 17 to generate pulses by the pulse width control circuit 19, a rectifier circuit 21 for rectifying and smoothing commercial AC, and rectification The switching transformer 23 for supplying power to the magnetron MG as a load by the switching element, the transistor 10 for switching the primary or coil of the switching transformer 23, and the on and off of the transistor 10 The switching element driver 16 to control, the detection comparator 22 which detects and compares a predetermined output from the switching transformer 23 and sends it to the pulse generator 25, and the secondary or coil of the switching transformer 23. Synchronization is detected and sent to the pulse generator 25 The synchronization detection part 22a is provided.

FIG. 3 is a circuit diagram showing an embodiment of the power supply unit 18, the pulse width control circuit 19, and the pulse generator 25 shown in FIG. 2. The power supply unit 18 smoothly outputs a constant power after changing AC into DC. The power supply transformer 30, the bridge rectifier 31, the smooth condenser 32, 33, and the regulator RE are provided.

In addition, the pulse width control circuit 19 includes a comparator 38, a diode 34 (Do), and a capacitor 35 (Co) for comparing the difference between the reference resistors 36 and 37 and the variable resistor VR ₁ . , Resistor 39 (Ro), etc., the pulse generator 25 has a diode (D ₁₀ ~ D ₁₂ ), a resistor (R ₁₀ ~ R ₁₃ ), a capacitor ( C ₁₁ ) is provided and a comparator OP ₁ is connected to a negative resistance terminal of the detection comparator 22, and a resistor R ₁₄ to R ₁₆ and a diode () are provided from the comparator OP ₁ . D ₁₃ ), the positive terminal of the comparator OP ₀ is connected via the capacitor C ₁₀ , and the triangular wave generator is connected to the positive terminal.

8 and 9 illustrate another embodiment of the present invention, which includes a rectifier bridge BG, a coil L ₁ , and a capacitor C ₁ , and includes a rectifier power supply unit 40 for outputting a constant power source, and rectification. The pulsation detection unit 41 having a resistor (R ₂ to R ₄ ), a Zener diamond (ZD), and a variable resistance (VR ₀ ) for detecting AC pulsation from the power supply unit, and the variable output and reference voltage of the pulsation detection unit 41. The pulse width control circuit 42 consisting of a resistor (R ₄ ~ R ₈ ), a comparator (OP), a capacitor (C ₂ ), a Zener diode (ZD ₂ ), a diode (D ₁ ) to control the pulse width by comparing A resistor (R ₉ ) (R ₁₈ to R ₂₀ ), a comparator (OP ₈ ), a diode (D ₂ ), and a capacitor connected between the pulse width control circuit 42 and the switching element driver 16 to generate a pulse. And a pulse generator 25 made of C ₆ .

The operation and effects of the present invention configured as described above are as follows.

That is, in the present invention, as shown in FIGS. 2 and 3, the output of the power transformer 30 from the power supply unit 18 becomes a pulse current through the bridge rectifier 31, and at the f side of the rectifier diode 31, The peak voltage is obtained by the diode 34 and the capacitor 35 of 19). This peak voltage is divided by a variable resistor and compared by the operational amplifier circuit 38, and the output of the capacitor is stabilized.

This output also varies the operational amplifier OP ₀ comparison input of the pulse generator 20.

At this time, the operational amplifier OP ₀ of the pulse generator 25 has an output of the pulse width control circuit 19 as a logic φ when the commercial pressure voltage is high, and thus the operational amplifier OP ₀ of the pulse generator 25. The comparison input is lowered to the-level, and the output of the operational amplifier OP ₀ is reduced through the switching element driver circuit 16 to reduce the on-time of the switching element 10.

Therefore, the magnetron on the load side will lower its output. In addition, if the current flowing between the anode A and the cathode K of the magnetron is Ibm, it is fed back through the current detector 22, and in the case where the output level is large through the operational amplifier OP ₁ , the operational amplifier ( Stabilize the circuit by lowering the-level of OP ₀ ).

4 is a characteristic curve of the voltage ebm between the anode A, the cathode K, and the current Ib of the magnetron, and the voltage ebm can be automatically determined.

Therefore, it is possible to design the output condition of the pulse generator 25 in consideration of such an operating condition of the load.

5 shows that the output of the pulse width control circuit 19 becomes a logic φ when the commercial power source applied to the present invention is momentarily interrupted, and is restored again in the normal state.

6 is a waveform diagram showing the operating conditions of the pulse generator 25, the switching element 10 and the like.

Here, V _CE is a collector-emitter voltage of the switching element 10, IC is a collector current of the switching element 10, V _BE is a base emitter voltage of the switching element 10, V ₀ is a pulse generator ( 25) is an output signal.

7 (a) shows that even if Vpp changes according to the commercial input voltage, the change in the maximum on time keeps the detection time t ₂ of Ibm at incubation, so that the load is applied by the constant power output together with Ibm. In the case of a microwave oven, cooking can be eliminated undercooked or overcooked without changing the input voltage.

In addition, (b) is a reference table showing the input variation of the microwave power supply circuit of the microwave oven equipped with the pulse width control circuit 19 of the present invention and the change-side change-based on the load side as experimental examples.

Meanwhile, in the second embodiment of FIGS. 8 and 9, the voltage divided by the resistors R ₂ and R ₃ in the pulse detection unit 41 is divided by the resistor R ₄ and the variable resistor VR ₀ . It is applied to the inverting terminal of the operational amplifier (OP) circuit on the pulse width control circuit 42 side.

At this time, the variable resistor VR ₀ is set so that the output terminal of the operational amplifier OP maintains the logic? Value near the peak of the pulse wave voltage wave, and this is the operation amplifier of the pulse generator 25 when the logic? The non-inverting input of OP ₈ is discharged to reduce the square wave output output from the operational amplifier OP ₈ so that the on-time of the switching element 10 by the switching element driver 16 is kept short and is supplied to the load. Will be reduced.

When the pulse current input from the pulse detector 41 is small, the output of the pulse width control circuit 42 becomes logic 1 so that the operational amplifier OP ₈ of the pulse generator 20 causes the voltage of the non-inverting terminal to increase. Thus, the driving pulse width of the switching element 10 is widened.

In addition, the operation waveform of each part at this time is shown as FIG.

The present invention is advantageous in that the switching power supply for driving a microwave can be stably driven by protecting the system circuits such as input voltage fluctuations and instantaneous power failures.

Claims (1)

A power supply section 18 connected to an AC power input terminal for supplying a constant DC power supply, a pulse width control circuit for detecting peak voltages from the power supply section and comparing it with a reference voltage, and the power supply section between the power supply section and the pulse width control circuit. A pulse generator for detecting an AC pulse of the pulse generator to detect the level of the input voltage, a pulse generator for generating a pulse by comparing the output of the pulse width control circuit with the output of the triangular wave generator, and switching according to the output level of the pulse generator A pulse width control circuit of a switching power supply device comprising a switching element driver for controlling the on-time of an element so that the output of the magnetron is added or subtracted.